Method and apparatus for independent control of brightness and color balance in display and illumination systems

• US 6,618,031 B1
• Filed: 02/26/1999
• Issued: 09/09/2003
• Est. Priority Date: 02/26/1999
• Status: Expired due to Term

• Current Assignee: Emerson Radio Corporation (Nimble Holdings Co. Ltd.)
• Original Assignee: Three-Five Systems, Inc.
• Inventors: Bohn, Jr., Lowell F., McKnight, Douglas J.
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Nguyen, Kimnhung
• Application Number:
  US09/258,512
• Time in Patent Office: 1,656 Days
• Field of Search: 345/83, 345/82, 345/77, 345/691, 345/88, 345/91, 345/692, 345/693
• US Class Current: 345/83
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/0275 Details of drivers for data electrodes, other than drivers for liquid crystal, plasma or OLED displays, not related to handling digital grey scale data or to communication of data to the pixels by means of a current
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 3/20 for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: H05B 45/24 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A drive circuit for a time sequential color LED based display device allows the overall brightness of a display device to be adjusted without affecting the color balance. The circuit includes a boost switching converter, which provides constant power to each of a plurality of different colored LEDs associated with a pixel, independent of the forward voltage across each LED. The boost switching converter receives a pulse width modulated drive signal for activating each LED, when enabled, during a frame. The on-time of the drive signal varies during each frame according to which LED is to be activated at a particular point in time, to provide the appropriate power to the LED. The LEDs are enabled sequentially during a frame by separate enable signals. The cathode of each LED is connected to a positive power supply voltage when the LED is enabled.

Claims

1. A circuit for controlling a pixel in a time-sequential color based display device, the circuit comprising:

a plurality of color elements associated with the pixel, each color element for displaying light of a different color;

a plurality of transistors, one for each of the color elements, each of the plurality of transistors having a source-to-drain path coupled in series with a corresponding one of the color elements between a power supply node and an output node, each of the plurality of transistors further having a gate coupled to a separate one of a plurality of enable signals, each enable signal for enabling the corresponding color element during each frame; and

a switching converter including;

an energy storage device having a first node coupled to receive a supply voltage;

a drive transistor having a source-to-drain path coupled in series between a second node of the energy storage device and a power supply reference voltage, the drive transistor further having a gate coupled to a drive signal, the drive signal for causing powering of each of the plurality of color elements during each of a plurality of frames;

a diode; and

a capacitor coupled in series with the diode, the series combination of the capacitor and the diode coupled in parallel with the energy storage device, a common node between the capacitor and the diode forming the output node.

2. A circuit according to claim 1, wherein the switching converter comprises a boost switching converter.

3. A circuit according to claim 1, wherein the switching converter comprises a flyback switching converter.

4. A circuit according to claim 1, wherein the drive signal has a different on-time associated with each of the plurality of color elements within each frame.